The present invention relates to sheet materials generally and more particularly relates to a sheet material suitable for use as a flexible, weatherable paint film.
Manufacturers have shown increasing interest in using paint films in lieu of spray painting for providing a decorative surface finish for parts, such as automobile body parts. This manufacturing technique reduces the environmental concerns associated with painting and has the potential to reduce manufacturing costs. An automobile body part utilizing a plastic paint film to provide a high quality base coat/clear coat automotive finish is disclosed, for example, in U.S. Pat. No. 4,810,540, which is incorporated by reference herein in its entirety. In producing the part, the paint film is typically formed into a contoured three-dimensional configuration corresponding to the shape of the outer surface of the part by suitable methods, such as by thermoforming.
Automotive manufacturers, for example, require that automotive parts have an exterior paint appearance which meets demanding performance and appearance specifications, such as weatherability, resistance to ultraviolet light degradation, high gloss, and high distinctness-of-image (DOI). For some applications, a paint film having an exterior surface that exhibits a low gloss or matte finish is desirable.
Heretofore, it has been difficult to produce a paint film having a uniform low gloss appearance where the paint film is formed into a complex three-dimensional configuration. Typically, the forming process imparts significant elongation to some areas of the paint film while leaving other areas substantially non-elongated. The amount of elongation impacts the exterior gloss of the paint film in such a manner that uniform gloss is difficult to achieve.
In U.S. Pat. No. 5,750,234 to Johnson, et al, a paint film having low surface gloss is provided by dispersing a particulate filler in the outer clear coat layer of the film, in conjunction with use of a matte finish carrier layer. During thermoforming, the particulate filler in the clear coat layer lowers the surface gloss of the outer clear coat. However, the Johnson patent does not solve the problem of poor gloss uniformity in a complex three-dimensional paint film where substantial differences in the amount of elongation experienced by different areas of the film exist. Additionally, adding a filler material to the clear coat layer can adversely affect weatherability and durability properties of the clear coat layer, such as scratch and mar resistance.
There remains a need for an improved method of applying a paint film finish to complex-shaped molded articles, such as highly contoured automobile body parts, that meets or exceeds the demanding performance and appearance specifications of part manufacturers. Specifically, there is a need for a method of providing a uniformly low gloss paint film finish for complex-shaped, three-dimensional molded articles.
The present invention provides a uniform low gloss paint film, and a method for forming such a paint film, suitable for surfacing complex-shaped three-dimensional molded articles. Despite differences in the amount of elongation experienced by different areas of the paint film of the present invention, the paint film exhibits a controllable, low gloss finish that is substantially uniform in appearance, regardless of extent of elongation.
The present invention provides a flexible, weatherable decorative sheet material that includes a decorative paint film, wherein the paint film has an inner surface and a weatherable outer surface, and an extensible mask layer releasably adhered to the outer surface of the paint. film. The extensible mask layer forms a protective film overlying the paint film and comprises a film-forming polymer component and at least one particulate filler dispersed in the polymer component. The film forming polymer component is preferably selected from the group consisting of polyurethane, polyolefin, polyester, polyamide, and mixtures thereof The extensible mask layer has a thickness of about 0.3 mil to about 3 mils.
Preferably, the particulate filler is selected from the group consisting of pigments, fumed silica, talc, calcium carbonate, clay, alumina, and mixtures thereof. In an exemplary embodiment, the particulate filler is present in the mask layer at a concentration of at least about 0.5 weight percent of the mask layer on a dry solids basis. Other exemplary embodiments utilize a filler concentration of at least about 1.0 weight percent or at least about 2.0 weight percent. The particulate filler has a mean particle size of up to about 20 microns.
The particulate filler concentration is preferably sufficient to controllably alter the gloss appearance of the underlying paint film after thermoforming and upon removal of the mask layer. Typically, the weatherable outer surface of the paint film has a 60 degree gloss of at least about 60 in dry film form prior to adhering the paint film to the mask layer. After application of the mask layer and heat and/or pressure, the outer surface of the paint film has a 60 degree gloss of less than about 30 after removal of the mask layer. Preferably, the outer surface of the paint film has a 60 degree gloss of less than about 20 after removal of the mask layer.
The paint film may comprise a single layer of a pigmented polymer or multiple layers including a clear coat layer of a transparent weatherable polymer and an underlying color coat layer of a pigmented polymer. The paint film may further include a color adjustment layer between the clear coat layer and the color coat layer. The sheet material may include additional layers, such as a thermoformable backing layer bonded to the inner surface of the paint film, and an adhesive layer bonding the backing layer to the inner surface of the paint film.
The present invention also provides a preform for in-mold surfacing of a part comprising the sheet material described above formed into a three-dimensional configuration. The forming step may comprise, for example, thermoforming the sheet material. The present invention further includes a composite-shaped part comprising the preform described above and a substrate of a thermoplastic polymer conforming to the three-dimensional configuration of the preform and adhered thereto.
The present invention also provides a method of controlling the gloss appearance of a paint film. The method includes providing a decorative paint film having an inner surface and an outer surface having an initial gloss value. The initial 60 degree gloss value is preferably at least about 60. An extensible mask layer is releasably adhered to the outer surface of the paint film. The extensible mask layer comprises a film-forming polymer component and at least one particulate filler dispersed in the polymer component as described above. Heat and pressure are applied to the paint film and the adhered mask layer in order to cause the mask layer to alter the gloss value of the adjacent paint film. Thereafter, the mask layer is stripped from the paint film to expose the paint film with the altered gloss value. Preferably, the altered 60 degree gloss value is less than about 30 after the removal of the mask layer, and most preferably less than about 20. In one embodiment. the step of applying heat and pressure comprises forming, such as thermoforming, of the paint film and the adhered mask layer. The forming process causes certain areas of the paint film to undergo an elongation of up to about 300 percent while leaving other areas of the paint film substantially non-elongated. Despite the differences in elongation experienced by different areas of the paint film, after the removal of the mask layer, the 60 degree gloss rating of the elongated areas of the paint film is within 10 gloss units of the gloss rating of the non-elongated areas.